Field of the Invention
The invention relates to a method and an apparatus for joint data-pilot tracking of navigation signal.
Description of the Related Art
A pilot channel is typically introduced to improve navigation signal tracking performance. A pilot signal does not have a modulated data bit and the problem of data-bit flip, thus a longer coherent-integration time can be used in pilot signal tracking, thereby improving tracking accuracy. In addition, pilot-channel carrier tracking employs a pure phase-locked loop, which is sensitive to data-bit flip and is much superior to, in terms of tracking sensitivity, a Costas loop employed by data-channel carrier tracking. However, in such pilot-only tracking mode, data-channel signal is not involved in tracking, resulting in energy loss.
Joint data-pilot tracking of navigation signal has been developed primarily based on two categories: data-pilot non-coherent accumulation and data-pilot coherent accumulation. However, the data-pilot non-coherent accumulation brings in squaring loss and the data channel adopts the Costas loop, all these affect the tracking sensitivity. The data-pilot coherent accumulation has optimal tracking performance at high carrier-to-noise ratios but it performs poorly at low carrier-to-noise ratios.